The present invention relates to a medical tube which is inserted into a living body, and more particularly to a medical tube used as an insertion section of a catheter for angiography or as an insertion section of an endoscope.
The insertion section of a catheter or endoscope is, when inserted into a living body, apt to be buckled due to the resistance acting against the inserting action. If such a catheter or endoscope is repeatedly used, its insertion section will be permanently bent.
Thus, if the insertion section of a catheter or endoscope is buckled or permanently bent when inserted, force is not properly transmitted from an operating section of the catheter or endoscope to the insertion section, thereby degrading the operational characteristic. If the insertion section buckled at a portion thereof is inserted into a blood vessel, the buckled portion will damage the peripheral wall of the vessel. With such an insertion section having a poor operational characteristic, the time for which the insertion section need be inserted will inevitably be longer, which will increase the patient's pain.
In order to facilitate the insertion of a medical tube for angiography, a stainless wire or plate may be embedded in the peripheral wall of the tube. However, the stainless material has a small elastic region with respect to stress. If a stress exceeding the elastic region is applied to the tube, the tube will be buckled and will be permanently bent after a long use.
The medical tube used as the insertion section of a catheter or endoscope, described above, is inserted into a blood vessel, alimentary canal, etc., so as to examine or treat the affected part. The tube should therefore be inserted into a blood vessel, alimentary canal, etc. without damaging the same. Further, a medical tube is needed which permits the distal end portion thereof to be curved in a desired direction at a desired part in the living body.
Conventionally, various medical tubes whose distal end portion can be curved are known, e.g., from Japanese Patent Disclosure (KOKAI) No. 59-48710 and Japanese Utility Model Disclosure (KOKAI) No. 59-2344. According to the prior art structures, a shape memory alloy arranged in the medical tube is deformed by heat applied thereto, whereby the distal end portion of the tube is curved.
However, the shape memory alloy arranged in the tube does not assume a preset shape at a normal room temperature and has a martensite structure wherein it can be plastically deformed by an external force. The tube will therefore be easily buckled due to the plastic deformation of the shape memory alloy. If the buckled tube is inserted through a blood vessel, alimentary canal, etc., it would damage the organ.